One statement I often see made by health gurus is that all calories are created equal.
“A calorie is a calorie”, “All that matters when it comes to weight loss is calories in vs. calories out”.
These claims are not at all surprising, since “conventional wisdom” has led people to believe that this is true.
Like I’ve said before on this blog, eating healthy is simple, but nutrition and metabolism are extremely complex, and all calories are absolutely not created equal, despite what you may have heard.
But before I get into that, let me explain what a calorie really is…
A calorie is a unit of energy. To be more precise, a calorie is the energy required to heat 1 gram of water by 1°C.
A “dietary” calorie (simply referred to as a Calorie) is actually the same as a kilocalorie, or 1000 calories. Therefore, a dietary calorie is the amount of energy required to heat 1 kilogram of water by 1° Celsius.
As we know, there are three different macronutrients that supply calories in the diet (alcohol also supplies calories, but I will not discuss that here).
A gram of carbohydrates provides 4 calories, a gram of protein also provides 4 calories, while a gram of fat supplies 9 calories.
Given that calories are supplied by different macronutrients, they are in a way very different depending on which foods they came from.
And if you consider the fact that these three macronutrients are metabolized in different ways, with different metabolic pathways, different metabolites, waste products, etc. etc. it’s not difficult to imagine the vastly different effects these macronutrients have on our bodies.
Let me discuss each one separately.
Dietary carbohydrates generally serve one purpose: to provide energy. Some are used to form parts of cellular structures, but that is a very small amount.
Carbohydrates, in fact, are the only macronutrient that humans can pretty much live without.
It is true that the brain and a few other tissues can only use glucose (a carb) for energy, but the fact is that the body can generate the glucose it needs through a process called gluconeogenesis.
Some of the nutrients that carbohydrate containing foods supply are essential, such as Vitamin C, but the carbs themselves are simply a form of energy.
Skipping carbs completely is something I definitely do not recommend. I suggest eating a variety of vegetables, occasional fruit, tubers and even some healthy grains for those who live an active lifestyle.
But I definitely do find the claim that 50-60% of energy should be supplied by carbohydrates to be shady and this does not seem to be based on sound science.
When carbohydrates are reduced in the diet, health tends to improve, at least for people who have a “broken” metabolism, such as overweight individuals and diabetics.
Low-carbohydrate diets have been shown to vastly improve cholesterol levels, lower triglycerides, blood sugar, insulin and blood pressure, cause substantial weight loss, and lead to a spontaneous drop in appetite and calorie consumption, without restricting food intake.
When low-carb diets are compared with standard low-fat diets, they win every time, despite the fact that the low-carb group can eat anything they want while the low-fat group is calorie restricted. Take a look at these studies if you don’t believe me: (1, 2, 3, 4, 5, 6, 7).
It seems that for people who have a propensity towards weight gain or diabetes, carb calories are the ones to reduce. For these people, getting the majority of calories from fat and protein seems to be the obvious choice.
Proteins, and the amino acids they contain, are the workhorses of the body. Proteins and amino acids form all sorts of structures, enzymes, hormones, receptors, etc. etc.
When excess protein is consumed, it is used as a source of energy, just like carbs and fat.
Protein is absolutely essential, and it is important to consume high-quality protein sources that contain all the necessary amino acids.
The calories in protein are not the “same” as calories from carbs and fat, because they tend to be used for structural and functional purposes instead of as energy.
However, many people do eat way more protein than they need, and for some people it can be a significant source of energy.
Protein is more satiating than other macronutrients, and therefore leads to less overall energy intake and increased weight loss. Additionally, the body uses more energy to metabolize protein, and therefore protein calories are absolutely not the same as calories from other macronutrients (8).
Fat is generally considered to be a source of fuel and a good form to store energy in, but it also has critical structural and functional roles in the body.
Consider the cell membrane, which is made in large part of fatty acids. Fatty acids and fat-soluble substances (such as cholesterol) form many hormones and play all sorts of functional roles.
In contrast to carbohydrates, fat is an essential nutrient. The essential fatty acids Omega-3 and Omega-6 are absolutely vital to humans, because the body can not produce them on its own.
Seeing how incredibly different roles these macronutrients play in the body, claiming that all calories are created equal is a massive oversimplification.
The calories in meat, for example, supplying a lot of protein and fat, but no carbs, will have a substantially different effect on the body than the calories in bread.
Even this article is overly simplifed, because these macronutrients have subcategories that make the picture even more complicated.
For example, the simple sugars glucose and fructose are metabolized very differently. The different amino acids also have varying effects, and the types of fat can also be very different.
To sum up, foods are more than simple sources of energy. The different macronutrients have different roles and are metabolized very differently. Therefore, the claim that “all calories are created equal” is nonsense.